Adenosine is a purine nucleotide that has been demonstrated to produce a number of physiological functions. In the cardiovascular system, adenosine causes vasodilation, hypotension, and reversal of tachycardia. Adenosine is currently used to treat ventricular arrhythmia. Adenosine is released during hypoxia and has been shown to protect the myocardium by increasing energy supply and reducing energy demand. In cardiac myocytes and other cell types, adenosine is released in large amounts during the reperfusion phase following ischemia. Reperfusion injury due to oxygen radicals is a major factor in infarct severity. Adenosine has been shown to reduce infarct size following ischemia-reperfusion in cardiac myocytes, indicating potential value in cellular protection. In the kidney, adenosine affects outer medullary blood flow, inner medullary blood flow, renin secretion, urine flow, and sodium excretion. Blockade of adenosine receptors in the kidney may be therapeutically useful in chronic renal disease. In the brain, adenosine attenuates neuronal degeneration of cells deprived of oxygen or glucose. This effect is mimicked by the non-selective adenosine agonist 5′-N-Ethyl-carboxamido-adenosine (NECA). In the striatum and hippocampus, adenosine antagonists have been shown to increase acetylcholine release, an effect therapeutically relevant to neurodegenerative diseases such as Alzheimer's Disease and Parkinson's Disease. In inflammatory conditions such as asthma, adenosine has been shown to stimulate bronchonstriction and to cause mast cell degranulation. Thus, adenosine receptor antagonists may have therapeutic utility in these situations. Adenosine has also been shown to down-regulate monocyte/macrophage pro-inflammatory functions. Accordingly, in certain types of inflammatory conditions, an adenosine receptor agonist may have therapeutic utility.
In view of the important role that adenosines play in many physiological processes and medical conditions, there is a need for materials and methods useful for the identification of agonists and antagonists selective for the specific types of adenosine receptors.